The Laws pertaining to on-the-line apply when the ball is between the goal-line and the adjacent 3-yard-line and has been played under control by an attacking player.
The attacker on-the-line must keep the ball moving. If the ball is stopped as a result of the actions of the defender, the attacker has a few moments to start the ball moving again.
Defenders must engage the attacker playing the ball on-the-line at the earliest opportunity and constantly while the ball is on-the-line. The defender is engaging with the attacker when they are in playing distance of the ball AND make a genuine attempt to play the ball. In most situations this will mean that the defender makes contact with the ball on a regular basis (i.e. at least every three seconds or so); however, it is possible (perhaps as a result of the body position adopted by the attacker) that the defender does not or cannot actually make contact with the ball. The umpire needs to decide whether the defender is making the best possible attempt to play (i.e. make contact) with the ball. The umpire should warn a team if it is failing to engage; if the team fails to respond, a penalty should be awarded against the defending team (see J-5).
Attackers and defenders must observe the Laws pertaining to Sneaking-on-the-Line. (See O-8).
When the ball is on-the-line (see J-1): the penalty for any infringement by a defender is the award to the attacking team of both a Point and the choice of a Free-Kick or Set-Piece-Bully on the 3-yard-line.
Any infringement by an attacker results in a goal-kick for the defending side.
In the event of infringements of a dangerous or abusive nature, further penalties may also be imposed. See C2-4.